1. Field of the Invention
The present invention relates to a non-coated polyester filament woven fabric for air bags. More particularly, the present invention relates to a non-coated polyester filament woven fabric useful for providing air bags for an automobile or aircraft having a very low gas-permeability even after a dry heat-aging over a long period of time, an excellent resistance to breakage even when the automobile or aircraft violently crashes, a superior functionality for safety and protection of an occupant in the automobile or aircraft from burns.
2. Description of Related Art
Air bags for automobiles and aircrafts are required to sufficiently protect occupants in the automobile or aircraft from shock when the automobile or aircraft crashes. Also, the air bags are required to present no risk of burns caused by inflation gas introduced thereinto and to have a high resistance to breakage when the automobile or aircraft crashes.
In order to provide an air bag with no risk of imparting burns to an occupant, it is necessary to reduce air permeability of the air bag-forming woven fabric. Also, in order to provide an air bag having a high resistance to breakage, it is necessary that the air bag-forming woven fabric has a high tensile strength, a high ultimate elongation, and a high burst strength.
Canadian Patent No. 974,745 discloses a non-coated, non-calendered nylon filament woven fabric for air bags. However, the resultant air bags produced from the above-mentioned nylon fabric exhibit an unsatisfactory air permeability and burst strength, because in this woven fabric, the yarn densities in warps and wefts are greatly different from each other and a tenter frame which causes a large residual strain and stress to remain on the fabric, was used.
For example, Japanese Unexamined Patent Publication (Kokai) No. 3-137,245 discloses a non-calendered, non-coated nylon 66 filament woven fabric usable for air bags. This woven fabric may have a low air permeability of 10 liters/dm.sup.2 /min (about 0.4 ml/cm.sup.2 /sec/0.5 inch Aq) or less determined under a pressure of 500 Pa, by applying a scouring procedure and a heat treatment thereto. In an example of the above-mentioned Japanese publication, a nylon 66 filament woven fabric having an air permeability of 3.4 liters/dm.sup.2 /min (about 0.14 ml/cm.sup.2 /sec/0.5 inch Aq) is disclosed. Also, this Japanese Publication discloses a woven fabric having a tensile strength of 2,300 to 3,300N/5 cm (about 141 to 202 kg/3 cm). However, the above-mentioned Japanese Publication is completely silent as to the durability of the air permeability and the burst strength of the air bag over a long period of time.
As a typical example of conventional non-coated polyester filament woven fabrics for air bags, U.S. Pat. No. 4,977,016 (Japanese Unexamined Patent Publication (Kokai) No. 4-2,835) discloses a non-coated polyester filament woven fabric not coated or not impregnated with a resin and having an air permeability of 0.5 ml/cm.sup.2 /sec/0.5 inch Aq or less.
Also, U.S. Pat. No. 5,010,663 (Japanese Unexamined Patent Publication (Kokai) No. 4-2,835) discloses a non-coated polyester filament woven fabric having an air permeability of 1.5 ml/cm.sup.2 /sec/0.5 inch Aq or less. In the above-mentioned publications, it is disclosed that since the polyester filaments have a low moisture absorption, when the polyester filament woven fabric is calendered, the calendered polyester filament woven fabric exhibits a poor recovery in bulkiness and a small change in air permeability in comparison with conventional calendered nylon filament woven fabric. However, the above-mentioned publications are completely silent as to particular means for more stabilizing the air permeability of the polyester filament woven fabric after dry or wet heat-aging over a long period of time. Also, these publications are silent as to the burst strength and durability of the fabrics. U.S. Pat. No. 4,921,735 (Japanese Unexamined Patent Publication (Kokai) No. 1-122,752) discloses a calendered non-coated polyester filament woven fabric for air bags having an air permeability of 0 to 0.53 ml/cm.sup.2 /sec/0.5 inch Aq. Nevertheless, this patent does not completely teach or suggest particular means for stabilizing the air permeability and the burst strength of the fabric after dry or wet heat-aging over a long period of time.
EP-A-0,442,373 discloses a non-coated, non-calendered polyester filament woven fabric which exhibits an ultimate elongation of 25% or more even when scouring and heat-setting treatments are applied thereto. In examples of the European publication, the resultant non-coated, non-calendered woven fabric realized an air permeability of 4.7 to 9.4 liters/dm.sup.2 /min (about 0.12 to 0.23 ml/cm.sup.2 /sec/0.5 inch Aq). However, the European publication is completely silent as to the stability in air permeability and burst strength of the woven fabric after dry or wet heat-aging over a long period of time.
When an air bag made from a conventional polyester filament woven fabric is left in a folded form in an automobile or aircraft over a long period of time during which the air bag is exposed several times to a high temperature and a high humidity, for example, in the summer and/or rainy seasons, the air permeability of the aged air bag is significantly increased from the initial air permeability thereof, as occurred in conventional air bags made from nylon 66 filament woven fabrics, and thus when an inflation gas is blown into the aged air bag, the amount of the inflation gas permeated through the air bag is increased and the inner pressure of the inflated air bag sometimes cannot reach a desired level. If the inner pressure of the inflated air bag is not sufficiently high, the air bag cannot exhibit a satisfactorily high shock-absorbing effect for the occupant in the automobile or aircraft, and thus the occupant is damaged upon crashing. Also, if the amount of the inflation gas leaked through the air bag is increased, the risk of burning the face of the occupant brought into contact with the air bag upon crashing is increased. Accordingly, it is important that the gas permeability of the air bag be maintained unchanged at a low level even if the air bag is aged in a dry or wet condition at a high temperature over a long period of time.
If the burst strength retention of a woven fabric is poor, and the resultant air bag is stored for a long period of time in an automobile or aircraft, the stored air bag sometimes exhibits a reduced burst strength and thus may be broken when a high pressure inflation is applied to the air bag.
Accordingly, it is important that the burst strength of the air bag be maintained unchanged at a high level even when the air bag is in a dry or wet condition at a high temperature over a long period of time.
Accordingly, it has been strongly demanded over a long time to provide a non-coated woven fabric for air bags which exhibits a satisfactory durability or persistency in air permeability and burst strength even after storage thereof under strict conditions for a long period of time.